Pharmacodynamics of vecuronium were evaluated in seven kidney transplant recipients and compared with seven patients with normal renal function. Vecuronium 0.12 mg.kg-1 was used for the initial dose and 0.03 mg.kg-1 for the second dose for each patient under general anesthesia with either isoflurane, sevoflurane or halothane plus nitrous oxide after induction by thiamylal. The effect of vecuronium was evaluated by a muscle relaxation monitor. The time to the maximum blockade (onset time) and the time of 25% recovery of the first twitch height (duration time) were measured after each administration of vecuronium in patients of both groups. The onset times after the initial and second doses were similar in both groups (180.0 +/- 15.5 sec for recipients versus 185.7 +/- 14.9 sec for patients of normal renal function). However, duration was significantly longer in recipients than in patients of normal renal function. Durations after the initial and second doses were 130 +/- 19 min for the initial dose and 86 +/- 12 min for the second dose in recipients, whereas they were 51 +/- 5 min and 37 +/- 5 min in patients of normal renal function. The prolonged durations of vecuronium in the kidney transplant recipient were speculated to be mainly due to delayed elimination of the drug and effect of cyclosporin, an immunosuppressive agent in the recipients. These results suggest that the titrated administration of vecuronium by keen monitoring of muscle relaxation is needed in the kidney transplant recipient to avoid unnecessary prolongation in duration of action.